PM NowCast

The NowCast uses hourly PM measurements to estimate a real-time AQI. The daily AQI for PM is calculated using a 24-hour average, meaning the true AQI can’t be calculated until that period is over.

To provide an AQI estimate in real time, the NowCast uses a weighted average of the past 12 hourly measurements. When hourly PM measurements change quickly, the most recent hourly measurements of the past 12 hours are weighted more heavily to better reflect the rapidly changing air quality conditions. However, when hourly measurements are very similar during the
past 12-hour period, each hour is weighted almost equally